One possibility is that 五 was originally written as five horizontal lines, similar to 一, 二, 三, and the obsolete 亖 (“four”), but in common writing the lines would blend together. Thus, two lines were turned vertical and the right one was shortened, to form one stroke with the middle horizontal line. An alternate hypothesis is that 五 originally resembled an X with a bar on top and a bar on bottom, as in 𠄡. This would have meant five because when counting on a single hand, one first counts to five and then crosses back the other way to ten.